Fluidizing electrode development apparatus



y 23, 1958 D. J. DONALIES 3,393,663

FLUIDIZING ELECTRODE DEVELOPMENT APPARATUS Filed July 21, 1966 2 Sheets-Sheet l INVENTOR. DANIEL J. DONALIES A TTORNEY July 23, 1968 D. J. DONALIES 3,393,663

FLUIDIZING ELECTRODE DEVELOPMENT APPARATUS Filed July 21, 1966 Z Sheets-Sheet 2 JNVENTOR. DANIEL J. DONALIES BY gf? ATTORNEY i United States Patent "ice 3,393,663 FLUIDIZING ELECTRODE DEVELOPMENT APPARATUS Daniel J. Donalies, Rochester, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed July 21, 1966, Ser. No. 566,944 12 Claims. (Cl. 118-637) ABSTRACT OF THE DISCLOSURE Xerographic development apparatus including a developer supporting plate positionable beneath at least a portion of a rotatable Xerographic surface having latent electrostatic images formed thereon. Development electrode wires are positioned in the development zone between the developer supporting plate and xerographic surface being developed so that upon rapid oscillation of the electrode wires and developer supporting plate, two-component developer in the development zone is vibrated into a fluidized mass for contacting and developing latent electrostatic images on the xerographic surface. A flow of developer through the developer zone is employed to ensure that fresh developer is in the development zone.

This invention relates in general to developing electrostatic images, and in particular, relates to apparatus for developing electrostatic images by utilizing vibrational forces to fluidize a two-component developer material.

In the practice of Xerography, as described in US. Patent No. 2,297,691, to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material aifixed to a conductive backing is used to support electrostatic images. In the usual method of carrying out the process, the Xerographic plate is electrostatically charged uniformly over its surface and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the original light pattern.

The latent electrostatic image can then be developed by contacting it with a finely divided electrostatically attractable material such as a resinous powder. The powder is held in image areas by the electrostatic charges on the layer. Where the charge is greatest, the greatest amount of material is deposited; and where the charge is least, little or no material is deposited. Thus, a powder image is produced in conformity with the light image of the copy being reproduced. The powder is subsequently transferred to a sheet of paper or other surface and suitably affixed to thereby form a permanent print.

The electrostatically attractable developing material commonly used in xerography consists of a pigmented resinous powder referred to here as toner and a coarse granular material called carrier. The carrier is usually coated with a material removed in the triboelectric series from the toner so that a triboelectric charge is generated between the powder and the granular carrier. Such charge causes the powder to adhere to the carrier. The carrier also provides mechanical control so that the toner can be readily handled and brought into contact with the exposed Xerographic surface. The powder particles are then attracted to the electrostatic image to produce a visible powder image on the xerographic surface.

The method of Xerographic developement of latent electrostatic images by fluidizing a two-component developer material in a development zone is described in 3,393,663 Patented July 23, 1968 US. patent application Ser. No. 566,847 copending herewith. As described in that case, a quantity of two-component developer material is vibrated beneath a latent electrostatic image. The vibrations are so rapid that they cause the mass of developer material to suspend itself in a fluidized mass or bed. As an image bearing xerographic surface is passed through the development zone, it is contacted by the fluidized or constantly moving developer and image areas of the Xerographic surface are developed with the toner material in the developer.

' The present invention constitutes new Xerographic development apparatus adapted to carry out the method of fluidized bed development as described above and incorporates advantageous features over other xerographic systems.

Early embodiments of fluidized bed development machinery, as described, for example, in the aforementioned patent application, had no provision for retoning carrier particles which became depleted of toner due to the toner deposition in image areas. The present invention, on the other hand, takes advantage of the inherent low friction properties of the fluidized developer material to continuously introduce freshly toned carrier particles into and out of the development zone. Due to the fluidized state of the developer in the development zone, the coeflicient of friction between the developer and the tray is reduced. A slight tilt of the fluidized bed will thus result in a flowing action of the entire fluidized bed in the direction of tilt. By introducing a supply of freshly toned carrier to the high side of the tilted development zone and concurrently collecting the depleted developer as it flows past the lower part of the development zone, freshly toned carrier can be supplied to image areas. This characteristic of a fluidized bed of developer to flow is advantageous for use in Xerographic machinery which requires a continuous supply of developer such as automatic machinery.

It has been found that the developer material may be fluidized by applying the vibratory force in an oscillating manner. If the oscillating force is applied about the axis of rotation of the xerographic drum rather than perpendicular to the drum axis, then the vibratory forces acting within the system are reduced.

Development electrodes are commonly used in Xerography to provide solid area development. The electrode consists of a grounded or biased member positioned as closely as possible to the xerographic surface to create an electric field in conjunction with the electrostatic image. Since development electrodes should be as close as possible to the Xerographic surface, it has been a continuous problem in automatic machines to provide an electrode that could be positioned close enough to the surface to create the electric field without interfering with developer flow. One approach to this problem has been to position an electrode plate or grid parallel to the Xerographic surface and spaced therefrom. With such an approach, if the electrode is too distant from the xerographic surface, the effect is reduced and solid area capabilities are minimized. If, on the other hand, the electrode is too close to the xerographic surface, the developer which flows parallel to the image and electrode is susceptible to being jammed between the closely spaced electrode and Xerographic surface. The presence of a development electrode within the development zone adjacent the image-bearing surface has another beneficial aspect. By simply constructing the electrode in the form of a wire network or the like, such wire network may be employed as the developer vibrating instrument. By contrasting the developer-supporting tray as used in former fluidized bed devices with the wire network of the present device, it is clearly seen that the mass of the vibration imparting elements will be greatly reduced. With the reduction of mass of the vibrational elements, the energy required to rapidly reciprocate the vibration imparting elements is reduced with corresponding decreases in noise and extraneous vibrations.

It is, therefore, an object of the present invention to develop latent electrostatic images.

It is a further object of the invention to improve fluidized bed development of xerographic images and to develop solid areas with fluidized bed development.

It is a further object of the present invention to improve fluidized bed development to accommodate a development electrode and to use the electrode to aid fluidizing the developer material.

It is a further object of the invention to recirculate freshly toned carrier through the development zone of a fluidized bed development system.

These and other objects of this invention are obtained by oscillating a developer tray and a strand type electrode about the axis of a xerographic drum to fluidize developer g material and by utilizing the flow characteristics of the fluidized material to recirculate developer material.

For a better understanding of the invention, as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings wherein:

FIG. 1 is a side view illustrating xerographic development apparatus constructed in accordance with the instant invention with parts broken away to show internal constructions.

FIG. 2 is a diagrammatic sectional view illustrating continuous and automatic xerographic reproducing apparatus including the development apparatus of the instant invention.

FIG. 3 is an upper right side perspective illustration of the rocker assembly shown in FIG. 2 with portions broken away to show internal construction.

FIG. 4 is a diagrammatic sectional view illustrating a portion of the development system according to the invention with a modified rocker assembly.

Essentially, the apparatus of the invention, as illustrated in the described embodiments, includes a developer sup port plate positioned beneath at least a portion of a latent electrostatic image-bearing drum and concentric therewith. Development electrode wires are positioned in the development zone between the plate and image-bearing surface. Means are provided to oscillate the electrode wires and developer supporting plate about the axis at the drum. When two-component developer is introduced between the plate and image, a vibratory motion is imparted thereto by the wires and plate and causes developer to suspend itself in a fluidized mass or bed in contact with the image. The vibration imparted to the developer and the fluidization thereof causes the individual particles to move continually into and out of contact with the imagebearing surface.

The transfer of the toner particles from their associated carrier beads to image areas principally occurs during this contact period. The deposition of toner to image areas is physically caused either by the attraction of the image exceeding the attraction of the carrier for the toner or the toner being jarred loose from the carrier by the force of contact as it strikes the xerographic surface whereupon the charge in the image areas attract the loose toner.

As the developer is suspended within the fluidized bed it has the appearance and characteristics of a liquid with the entire bed of developer being of a substantially homogenous density throughout. This uniform density across the entire development zone insures the presentation of even quantities of developer to all portions of the image across the xerographic surface. Consequently, the possibility of underdeveloped strips of image areas caused by the uneven presentation of developer to the image area is minimized.

The developer composition may be of the conventional type as presently employed in commercial xerographic machines utilizing cascade development. Such a composition is defined, for example, in Walkup Patent 2,618,551. An example of such a composition comprises carrier beads of glass or steel covered with and encased in a suitable coating such as vinyl chloride which imparts the necessary triboelectric properties to the toner upon contact therewith. The toner usually is a pigmented resinous material or the like which is used to develop xerographic images. The first embodiment of the present invention is adapted to develop latent electrostatic images formed on a xerographic surface shaped in the form of a drum 10. The drum 10, as shown in FIG. 1, is mounted for rotational movement upon a main drum drive shaft 12 driven by any suitable power source, not shown. This rotation of the drum permits a latent electrostatic image, formed on its surface, to sequentially pass through a xerographic development zone 14.

Also positioned on the shaft are a pair of end plates 16, each of which is apertured at 18 for oscillatory motion about the shaft. The end plates are positioned adjacent the opposite faces of the drum and are secured together by an arcuate plate 20, shaped concentric with the drum surface. The arcuate plate functions to support a particulate developer material in proximity to the xerographic surface of the drum during the performance of its developing function and may also impart a vibration to the developer.

A series of development electrode wires 22 also span the two end plates 16, and are also concentrically oriented with respect to the drum 10 and arcuate plate 20. The spacing between the wires is such that developer may easily pass therethrough. These electrode wires are secured in the end plates by cut out sections 24 in the end plates and are mounted through insulating strip barriers 26 of polyurethane foam or the like. The electrode wires are then either electrically connected to a source of potential 27 or a ground for the establishment of an electric field adjacent the drum. In addition to providing an electrode field adjacent the drum, the wires also act when oscillated with the end plate to create the principal source of vibration to the developer in the development zone.

An oscillatory motion is imparted to the end plates 16, arcuate plate 20, and electrode wires 22, by any convenient motion producing assembly. One such assembly as illustrated herein includes a linkage arm 28 formed with an integral bearing 30 and 34 at each end. The first bearing 30 is pivotally mounted on a stud 32, formed exteriorly on one of the end plates. The second bearing 34, is pivotally mounted on a similar stud 36, formed on a slightly off center portion of a motor means 38. As such, on rotation of the motor means, reciprocation is imparted to the linkage arm 28 and end plates 16. The end plates, by reason of their mounting on the main drive shaft 12, are thus oscillated concentric with the drum. This oscillation is so rapid that the mass of twocomponent developer located between the drum and arcuate plate suspends itself in a fluidized mass or bed due to the vibration imparted by the oscillating electrode wires and arcuate plate. This fluidized mass or bed will move into contact with the image on the drum.

Positioned above the development zone 14 is a developer storage tank 40. This tank is formed as a box with an open top 42, for the reception of additional twocomponent developer. The lowermost portion is formed with an aperture 44, for feeding the two-component developer to the development zone between the drum and arcuate plate. A flexible, tube-like connecting element 46 extending the length of the tank and arcuate plate guides the developer flow from the tank to the development zone. It is noted that the lowermost face 48, of the developer storage tank is angled towards the aperture to thus facilitate a gravity feed developer flow in the direction of the connecting element and development zone.

The overall orientation of the end plates 16 is such that flow of developer is generally downhill from the storage tank to the reception tray 50. This tilting of the end plates and associated arcuate plate, when taken with the raised developer storage tank, defines a gravity feed system to ensure that freshly toned developer is continually being passed through the development zone. A developer reception tray serves to collect the developer which has flowed through the development zone.

Shown in FIGS. 2-4 is a xerographic machine embodying the present invention constructed for continuous and automatic operation. The elements of this machine are all conventional in the xerographic art with the exception of the development station which forms the basis of the present invention. For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the xerographic surface as seen in FIG. 2 may be briefly described as follows:

A charging station A, at which a uniform electrostatic charge is deposited on the photoconductive layer of the Xerographic drum;

An exposure station B, at which the light or radiation pattern of copy to be reproduced is projected onto the drum surface to dissipate the drum charge in the exposed areas thereaof to thereby leave a latent electrostatic image of the copy to be reproduced;

A developing station C, which forms the basis of the present invention, at which a xerographic developing material, including toner particles having an electrostatic charge opposite to that of the electrostatic latent image, are moved into contact with the drum surface, whereby the toner particles adhere to the electrostatic latent image to form a xerographic powdered image in the configuration of the copy being reproduced;

A transfer station D, at which the xerographic powder image is electrostatically transferred from the drum surface to a transfer material or a support surface; and

A dum cleaning and discharge station E, at which the drum surface is brushed to remove residual toner particles remaining thereon after image transfer, and at which the drum surface is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.

The development station is constructed to two major sections, a rocker assembly 52, and a developer housing assembly 54.

The rocker assembly, shown in perspective in FIG. 3, is formed with two end plates 116 provided with apertures 118 for a rockable mounting on the main drum drive shaft 112. Development electrode wires 122 span the space between the end plates adjacent and concentrically positioned with respect to the drum. The electrode wires are secured in their positions by cut out sections 124 in the end plates and are mounted through suitable insulating strip barriers 126 of polyurethane foam or the like. The electrode wires are then electrically connected to a suitable source of high potential 127 for creation of a field adjacent the latent electrostatic image on the drum. The electrode wires, when oscillated, also act as developer agitators to cause the vibrated developer particles to suspendthemselves in a fluidized mass or bed for contacting, and consequently developing, the image on the drum.

In order to accomplish a continuous flow of two-component developer through the development zone 114 adjacent the image, the rocker assembly 52 is fitted with various guide plates. An L-shaped member 56 is secured between the end plates with its longer leg 58 formed in a curve, concentric with the drum and electrode wires. This leg serves as a developer supporting plate which supplements the developer agitation and also divides the rocker assembly into an upper and lower compartment for guiding the developer flow. A J-shaped plate 60 is also secured between the end plates with a curved portion 61 acting as a developer reversing guide to direct the developer from the development zone 114 back toward the developer housing assembly 54. The straight portion of plate 60 in association with the lower face of the member 56 also aids in guiding developer towards the developer housing assembly 54.

T he developer housing assembly 54 serves the purpose of accepting developer from, and refeeding it to, the rocker assembly 52 to constitute a closed developer recirculation system. This housing assembly has side walls, not shown, secured to any fixed part of the machine housing. Surrounding surface 62 retains the developer in the closed system.

In the lowermost region of the developer housing assembly is a developer sump 64 filled with a supply of twocomponent developer. A suitable toner dispenser 66 is formed above the sump to dispense new toner into the system.

A chute 68 formed by the front surface 70 of the developer housing assembly and an intermediate plate 72 spanning the side walls, gravity feeds developer into the rocker assembly 52. In order to move developer from the sump 64 to the top of the chute 68 a bucket conveyor assembly 74 mounted on an idler roller 76 and a drive roller 78 isprovided to span this distance.

An upper developer input space 80 and lower developer output 82 space bridge the developer housing assembly and rocker assembly. To keep these spaces separate and to allow for movement of the rocker assembly relative to the developer housing assembly, sheets 84, 86, 88 and of a flexible material as buna-N on silk are employed. These sheets are secured to each other and to the various parts of the machine by any commercially available adhesive material or the like. Side sheets 84 seal the entire space on the sides bridging these two assemblies. Three substantially horizontally disposed sheets, an upper 86 intermediate 88 and lower sheet 90 separate the input and output spaces. The upper sheet 86 is secured between the front surface 70 of the developer housing assembly and a supplemental top bar 92 spanning the end plates. The intermediate sheet 88 is secured between the intermediate plate 72 and the shorter leg of the member 56. These two sheets form a continuation of the chute 68 to the development zone 114. The lower sheet 90 is secured between the plate 60 and the section of the sump 64 adjacent the plate 60. The intermediate sheet 88 and lower sheet 90 thus form the guideway from the developer output space 82 to the sump 64. Consequently, a closed developer recirculation system is formed from the sump 64 to the top of the chute, through the chute 68 and input space 80 to the development zone 114, around the curved portion of the plate 60 to the output space 82 and finally back to the sump 64.

The motion imparting elements for this development system are positioned on the near side of the development station, as viewed in FIG. 3. These drive members may be of any suitable type with one motor for moving the bucket conveyors and a second motor means 138, shown in FIG. 3, for oscillating the rocker assembly at a high vibratory rate. The various other processing stations may be driven by any suitable driving means as found in known xerographic machines. With respect to the mechanisms for oscillating the rocker assembly, attention is'directed to FIG. 3. A high speed motor means 138 is mounted on a fixed portion of the machine. The mounting may be through suitable shock absorbing elements to minimize vibrations through the machine. Eccentrically mounted on the motor drive plate 94 is a linkage arm 128 formed at each end with an integral bearing member. The first bearing member 130 on the linkage arms is pivotally mounted on a stud 132 integral with a rocker assembly about the main drive shaft upon which it is mounted. It has been found desirable to attach the linkage arm to the center of percussion of the end plate to thus minimize unwanted vibrations.

In operation, the development station is set in motion with a quantity of two-component developer in the sump. As the rocker assembly oscillates, the bucket conveyor is continually supplying developer from the sump to the top of the chute. Gravity feeds the developer down the chute, through the input space and into the development zone for fluidization and development. The rocker assembly is offset slightly from the horizontal so that developer entering the development zone from the chute, which is fluidized by the vibratory action of the L-shaped member and agitator-electrode wires, is also caused to have a mass flow down the L-shaped member, toward the curved portion of the J-shaped plate. The developer, which is maintained in its fluidized state in the lower half of the rocker assembly by the agitation of the flat portion of the J-shaped plate, continues its mass flow down the J-shaped plate past the output space and into the sump. It is further noted that the flat portion of the J-shaped plate is slightly tilted from the horizontal, opposite from the tilt of the L-shaped member to permit this reversal of mass flow. During this time of development, the bucket conveyor assembly has been continually bringing developer from the sump to the top of the chute to maintain a continuous mass flow of developer through the development zone.

In FIG. 4 is shown a modification with an L-shaped member 256 having its longer developer supporting leg 258 formed with a saw-toothed cross section. In this embodiment, an increasing cross sectional area is created in the direction of mass developer flow from the uppermost to lowermost end of the rocker assembly. By using this saw-tooth plate, the fluidized developer will seek the greater cross sectional area. This modification thus tends by virtue of its cross sectional configuration, to direct the flow of the fluidized developer down the arcuate plate and minimize any uphill movement of the fluidized developer.

With respect to the electrode wires, two or more concentric sets of wires may be employed to improve solid area coverage. Any elongated conductive elements may be employed as the vibrating electrode, as by example, wire strips, an electrode screen, or even a perforate metallic plate so long as there is sufficient spacing to allow the developer movement between the image and arcuate plate.

While the present invention as to objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby; but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. Xerographic developing apparatus for developing latent electrostatic images on an image-bearing member with a two-component developer material comprising carrier particles and an electrostatically attractable powder including:

support means positioned adjacent a xerographic development zone beneath at least a portion of a latent electrostatic image-bearing member, the support means being capable of supporting a quantity of twocomponent developer material thereon,

vibratory means positioned in the development zone between the support means and image-bearing member being developed so as to be immersed in developer material on the support means and means to move the vibratory means through the developer material in the development zone sufficiently to fluidize the developer material into a fluidized mass in contact with the image-bearing member to be developed.

2. The apparatus as set forth in claim 1 wherein the vibratory means is -a development electrode constructed of a conductive material adapted to effect the electric fields of the latent electrostatic image-bearing member.

3. The apparatus as set forth in claim 1 wherein the vibratory means is of a conductive material biased to a potential the same as that on the image areas of the latent electrostatic image-bearing member.

4. The apparatus as set forth in claim 1 wherein the vibratory means is a grounded conductive member.

5. The apparatus as set forth in claim 1 wherein the vibratory means is apcrtured to permit the movement of developer between the support means and the latent electrostatic image-bearing member.

6. The apparatus as set forth in claim 1 wherein the vibratory means includes a series of spaced parallel conductive wires.

7. Xerographic developing apparatus for developing latent electrostatic images on a drum shaped imagebearing member with a two-component developer material comprising carrier particles and an electrostatically attractable powder including:

shaft means adapted to support a drum shaped imagebearing member for rotation about its axis,

support means suspended from the shaft means and capable of supporting a quantity of two-component developer material adjacent at least a portion of the surface of the image-bearing member,

and vibratory means positioned between the support means and the image-bearing member and adapted to oscillate about the shaft to fluidize the developer material into a fluidized mass in contact with the image-bearing member to thereby effect development of latent electrostatic images on the imagebearing member with developer material adjacent the vibratory means and the support means.

8. The apparatus as set forth in claim 7 wherein the support means is constructed with a saw-toothed cross sectional configuration to facilitate developer flow across the support means.

9. The apparatus as set forth in claim 7 wherein the vibratory means is a development electrode constructed of a conductive material adapted to affect the electric fields produced by the latent electrostatic image.

10. The apparatus as set forth in claim 9 wherein the developer support means is oriented to facilitate the gravity flow of developer thereacross.

11. The apparatus as set forth in claim 10 and further including:

developer input means operatively associated with the space above the developer supporting means to bring fresh developer material onto the support means,

a reception means positioned to collect developer which has flowed beyond the space above the support means,

and transport means to move developer from the reception means and to the developer input means, whereby the developer input means, the space above the support means, the reception means and transport means form a developer material recirculation system.

12. The apparatus as set forth in claim 1 and further including means interconnecting the support means and vibratory means so that the support means moves concurrently with the vibratory means.

References Cited UNITED STATES PATENTS 2,753,796 7/1956 Wood et al.

2,901,374 8/1959 Gundlach 118-637 XR 2,927,554 3/1960 Oldenboom 118-637 3,008,826 10/1961 Mott et al 118-637 XR 3,013,890 12/1961 Bixby 118-637 XR 3,263,234- 7/1966 Epstein et a]. 118-637 XR 3,295,440 1/1967 Rarey et a1. 118-637 XR CHARLES A. WILLMUTH, Primary Examiner.

PETER FELDMAN, Assistant Examiner. 

